(184j) Mosaic Ion-Exchange Resins for Reducing the Overpotential for Water Dissociation in Bipolar Junctions for Electodeionization Separations
AIChE Annual Meeting
2016
2016 AIChE Annual Meeting
Liaison Functions
Undergraduate Research Forum II
Monday, November 14, 2016 - 2:45pm to 3:00pm
from water using an applied electric field, ion-exchange membranes, and ion exchange resin bed
in the diluent stream. [1] The porous ion-exchange resin bed reduces the purified stream
resistance, the largest resistance in the system, by conducting ions across the immobilized bed
and by dissociating water to generate H+ and OH- ions for current flow through the stack. Water
dissociation in the ion-exchange resin bed occurs in nanometer thin bipolar junctions in the resin
bed. [2-4] These junctions consist of oppositely fixed positive charges that generate an internal
electric field for dissociating water. Most ion-exchange resin beds for EDI employ commercially
available cation and anion ion-exchange resins mixed together, but such mixing of the different
beads results in underutilized resins because few fixed anionic and cationic groups form effective
bipolar junctions. The consequence of poorly formed bipolar junctions results in energy
inefficient water desalination via EDI.
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In this work, mixtures of thin cation and anion polymer electrolyte brushes were thermally
grafted to silicon wafer and fumed silica nanoparticle surfaces to realize thin film mosaic ion-
exchange materials for EDI. Grafting the oppositely charged ion conductors to the same substrate
leads to a greater probability of opposite fixed charges being in close proximity for water
dissociation. The process to prepare the mosaic materials started with thermally grafting mono-
hydroxy terminated non-ionic polymer brushes to the substrate via a condensation reaction under
an inert environment. Then, subsequent ionization reactions (e.g., Menshutkin, acetyl
sulfonation, or thermal decomposition/acid catalyzed hydrolysis) [5-7] converted the brushes
into anionic and cationic polymer electrolytes. Verification of brush grafting and introduction of
ionic moieties was made using water contact angle measurement and Fourier transform infrared
spectroscopy (FTIR). Ionic conductivity of the homo- and mixed-polymer electrolyte brushes to
interdigitated electrodes was conducted via electrochemical impedance spectroscopy. Future
studies aim to incorporate the mosaic materials for resin-wafer EDI.